I have a young 18" redtail that I keep in a 450. It used to have tankmates but, I had to remove my "keepers", when it was 16", due to the RTCs appetite. In a week it ate 4 12"+ channel cats. That was less than 3 months ago. This species would only do well with fish that are not only its size, but those that can keep pace with its growth rate. Another contention to deal with is filtration. I had a 500 gal W/D on the 450 and couldn't keep this single-fish tank clean. Now I run a 1200gal bead filter running 1650gals/hr. I'm already planning on where to put the fish in my 650 when the RTC outgrows the 450. This is definitely not a fish to plan on keeping in a 240.